The invention concerns a sample holder for holding and transporting a sample vial within an NMR apparatus, comprising an outer shell and a continuous hollow space which is disposed inside the outer shell and extends along its axis, for receiving the sample vial, and an automatic supply device with an inventive sample holder for automated exchange of NMR sample vials, and methods of operation thereof.
A sample holder of this type is disclosed in U.S. Pat. No. 6,686,740 B2.
In NMR spectroscopy and, in particular, its industrial applications, large numbers of NMR samples must be measured automatically, i.e. without manual aid, in order to reduce personnel and improve the rate of utilization of the very expensive NMR spectrometers.
Such automated devices generally comprise a sample container which contains the NMR sample vials to be measured, with the measuring substances contained therein, a transport device, which grasps the sample holder containing the sample vial and transports it to the upper end of the room temperature bore (RT bore) of the NMR magnet, or a transport robot that removes the sample vial from a sample container and transports it to a supply device which inserts the sample vial into a sample holder, with the transport robot then transporting the sample holder, including sample vial, to the upper end of the RT bore, where the sample holder, including sample vial, is received by an air cushion device, transported on an air cushion from the upper end of the RT bore to the measuring chamber inside an RT bore, and returned to the upper end of the RT bore after measurement.
The air cushion device cooperates closely with a “docking device” (dock unit) which can i.a. receive and fix the probe head. The dock unit is located inside the RT bore and extends along its entire length. It contains the RT shim system and any gradient coils and has a cylindrical opening at its lower end into which the desired probe head can be inserted and fixed. The upper part of the dock unit has a cylindrical tube with an opening which opens to the outside at the upper end and through which the sample vial may be transported down to the measuring chamber. Compressed air is supplied below at the dock unit, which rotates the sample vial by means of an air turbine and also generates an air flow for the air cushion device. This air flows upwards along the tube that leads to the cylindrical opening at the upper end of the dock unit and escapes to the outside.
The maximum outer dimensions of the sample holder are important for the correct function of the air cushion device. It must fit into the upper opening of the dock unit with little play to prevent an excessive amount of air from escaping to the side. This produces an air cushion below the sample holder on which the sample holder including sample vial may be supported and slide downwards and upwards by reducing or increasing the air pressure.
There is an associated sample holder for any sample vial diameter, which is constructed such that its outer dimensions are preferably the same, irrespective of the diameter of the sample vial.
So-called “spinners” and “shuttles” are currently used as sample holders. In a spinner, the sample vial is rigidly clamped in the spinner, which, in turn, is formed such that it can be inserted into the upper opening of the dock unit with little play, and additionally also comes to rest exactly on the air turbine of the dock unit. The sample vial is thereby correctly positioned and centered. If required, the sample vial including spinner may be rotated using the air turbine in order to cancel inhomogeneities in the static magnetic field B0. This requires, however, that the spinner and the sample vial have a very high axial symmetry and their symmetry axes are disposed exactly on top of each other to produce rotation about a stable axis of rotation.
In the device of U.S. Pat. No. 6,686,740 B2, the sample vial whose diameter is preferably in a range between 1 and 3 mm, is loosely disposed in the shuttle, wherein a sleeve which closes the upper opening of the sample vial comes to rest on a shoulder within the shuttle. For this reason, the sample vial cannot fall downwards out of the shuttle. Loose positioning of the sample vial in the shuttle provides axial lateral and downward flexibility which considerably decreases the danger of breaking the sample vial during transport into the measuring chamber. The outer diameter of the shuttle is also dimensioned such that it can be inserted with little play into the upper opening of the dock unit. Rotation of the sample vial is not provided in this case. The outer shape of the shuttle is preferably selected to be the same as that of the spinner such that both sample holders, spinner and shuttle may be appropriately supported on the air turbine of the dock unit.
The sleeve at the top of the sample vial may also be used to hermetically seal the measuring substance inside the sample vial from the outside, in order to prevent the measuring substance from evaporating. It also permits application of an identification code (e.g. DOT matrix code) on the upper surface of the sleeve. Such an identification code is very convenient for automated sample exchange, since it defines i.a. the required adjustments of the NMR parameters during the measurement.
In some of the conventional devices for changing the NMR sample vial, each sample vial to be measured is initially manually associated with one respective sample holder (either spinner or shuttle) into which it is inserted. A transport device subsequently moves one of the sample holders, including the sample vial, from the sample container to the upper outlet of the docking unit where it is transported by the air cushion device into the measuring area.
These devices have the following serious drawbacks. Since the unit consisting of sample holder and sample vial requires a storage space that is up to 25 times larger than the sample vial alone, the sample containers must either be very large or be provided with fewer units, which is highly disadvantageous. Moreover, each sample vial requires its own sample holder such that a large number of “spinners” or “shuttles” must be provided which involves relatively high costs.
Moreover, manual supply of the sample holder with a sample vial is time-consuming and is an additional burden for the staff, and should therefore be prevented to optimize automated operation.
In order to avoid these drawbacks, modern devices automatically supply the sample holder with a sample vial and also transfer the sample holder including sample vial to the air cushion device. Supply is effected with a controlled supply robot. It grasps an individual sample vial from the sample container which exclusively contains sample vials, and inserts it from above into the sample holder. When the sample holder is a conventional spinner, the sample vial must normally be pushed through a rubber ring or another passive clamping device which is located inside the spinner and is designed to fix the sample vial. Considerable frictional forces are thereby produced between the sample vial and the clamping device. The supply robot subsequently transfers the sample holder including sample vial to the transport device which disposes this unit onto the air cushion above the RT bore of the magnet, and further handling is effected by the air cushion device.
After measurement, the sample holder including sample vial are transported to the top by the air cushion device, taken over by the transport device and returned by the latter to the supply robot which removes the sample vial from the sample holder. This process is associated with considerable friction forces when a conventional spinner is used. If the supply robot performs this process by rigidly clamping the upper end of the sample vial and subsequently drawing the sample vial out of the spinner, the sample vial can be easily broken. For this reason, the supply robot must have access to the lower end of the sample vial in order to push the sample vial out of the rubber ring or the passive clamping device through one upward pushing motion. The robot must subsequently move again upwards, grasp the loose sample vial and return it to the sample holder.
In the above-described device it is therefore important that the sample vial is inserted and removed by one pushing action each, since only in this way can the danger be minimized that the sample vial breaks or the gripper slides off the tube.
These devices have the following disadvantages. The supply robot must have access to the lower end of the sample vial when the sample vial is removed from the spinner, in order to release the sample vial from the clamping action of the spinner through one pushing motion from below.
In addition to the supply robot which is also responsible for transporting the sample vial from the sample container to the supply device, the device also requires a transport device i.e. a total of two automated systems.
Moreover, the overall device requires a large amount of space as well as its own, sometimes very large, assembly frame.
These devices additionally use conventional spinners as sample holders, as are used for manual operation, or spinners whose function resembles that of conventional spinners, which has the following further disadvantages. The force required by the device for inserting the sample tube into such a spinner is relatively large. This force is a consequence of the high contact pressure between the spinner and the sample vial which is required to obtain high precision coincidence between the symmetry axes of the sample tube and of the spinner in order to assure proper rotation. The large contact pressure generates large frictional forces between the spinner and the sample vial and wears the spinner, in particular, of the second described device that has a supply robot and requires one single spinner for all sample vials of the same diameter.
It is the underlying purpose of the invention to propose a sample holder in an automatic supply device for changing NMR sample vials that avoids the above-mentioned disadvantages, has a very compact construction, and can be mounted requiring little space.